D. J. Alexander

A review of avian influenza in different bird species.

Only type A influenza viruses are known to cause natural infections in birds, but viruses of all 15 haemagglutinin and all nine neuraminidase influenza A subtypes in the majority of possible combinations have been isolated from avian species. Influenza A viruses infecting poultry can be divided into two distinct groups on the basis of their ability to cause disease. The very virulent viruses cause highly pathogenic avian influenza (HPAI), in which mortality may be as high as 100%. These viruses have been restricted to subtypes H5 and H7, although not all viruses of these subtypes cause HPAI. All other viruses cause a much milder, primarily respiratory disease, which may be exacerbated by other infections or environmental conditions. Since 1959, primary outbreaks of HPAI in poultry have been reported 17 times (eight since 1990), five in turkeys and 12 in chickens. HPAI viruses are rarely isolated from wild birds, but extremely high isolation rates of viruses of low virulence for poultry have been recorded in surveillance studies, giving overall figures of about 15% for ducks and geese and around 2% for all other species. Influenza viruses have been shown to affect all types of domestic or captive birds in all areas of the world, but the frequency with which primary infections occur in any type of bird depends on the degree of contact there is with feral birds. Secondary spread is usually associated with human involvement, probably by transferring infective faeces from infected to susceptible birds.

Avian influenza: recent developments

This paper reviews the worldwide situation regarding avian influenza infections in poultry from 1997 to March 2004. The increase in the number of primary introductions and the scientific data available on the molecular basis of pathogenicity have generated concerns particularly for legislative purposes and for international trade. This has led to a new proposed definition of ‘avian influenza’ to extend all infections caused by H5 and H7 viruses regardless of their virulence as notifiable diseases, although this has encountered some difficulties in being approved. The paper also reviews the major outbreaks caused by viruses of the H5 or H7 subtype and the control measures applied. The zoonotic aspects of avian influenza, which until 1997 were considered to be of limited relevance in human medicine, are also discussed. The human health implications have now gained importance, both for illness and fatalities that have occurred following natural infection with avian viruses, and for the potential of generating a reassortant virus that could give rise to the next human influenza pandemic.

Recombination Resulting in Virulence Shift in Avian Influenza Outbreak, Chile

Influenza A viruses occur worldwide in wild birds and are occasionally associated with outbreaks in commercial chickens and turkeys. However, avian influenza viruses have not been isolated from wild birds or poultry in South America. A recent outbreak in chickens of H7N3 low pathogenic avian influenza (LPAI) occurred in Chile. One month later, after a sudden increase in deaths, H7N3 highly pathogenic avian influenza (HPAI) virus was isolated. Sequence analysis of all eight genes of the LPAI virus and the HPAI viruses showed minor differences between the viruses except at the hemagglutinin (HA) cleavage site. The LPAI virus had a cleavage site similar to other low pathogenic H7 viruses, but the HPAI isolates had a 30 nucleotide insert. The insertion likely occurred by recombination between the HA and nucleoprotein genes of the LPAI virus, resulting in a virulence shift. Sequence comparison of all eight gene segments showed the Chilean viruses were also distinct from all other avian influenza viruses and represent a distinct South American clade.

A molecular epidemiological study of avian paramyxovirus type 1 (Newcastle disease virus) isolates by phylogenetic analysis of a partial nucleotide sequence of the fusion protein gene

A sequence 375 nucleotides in length, which included the region encoding the cleavage activation site and signal peptide of the fusion protein gene, was determined for 174 isolates of Newcastle disease virus (avianparamyxovirus type 1). These were compared with the sequences of 164 isolates published on GenBank, and the resulting alignment was analysed phylogenetically using maximum likelihood. The results are presented asunrooted phylogenetic trees. Briefly, the isolates divided into six broadly distinct groups (lineages 1 to 6).Lineages 3 and 4 were further subdivided into four sublineages (a to d) and lineage 5 into five lineages (a to e).Considerable genetic heterogeneity was detected within avian paramyxoviruses type 1, which appears to beinfluenced by host, time and geographical origin. It is concluded that by using this dataset it will be possible totype future virus isolates rapidly on the basis of their nucleotide sequence and make inferences about theirorigins.

SUMMARY OF AVIAN INFLUENZA ACTIVITY IN EUROPE, ASIA, AFRICA, AND AUSTRALASIA, 2002–2006

Abstract Between December 2003 and January 2004 highly pathogenic avian influenza (HPAI) H5N1 infections of poultry were declared in China, Japan, South Korea, Laos, Thailand, Cambodia, Vietnam, and Indonesia. In 2004 an outbreak was reported in Malaysia. In 2005 H5N1 outbreaks were recorded in poultry in Russia, Kazakhstan, Mongolia, Romania, Turkey, and Ukraine, and virus was isolated from swans in Croatia. In 2004 HPAI H5N1 virus was isolated from smuggled eagles detected at the Brussels Airport and in 2005 imported caged birds held in quarantine in England. In 2006 HPAI was reported in poultry in Iraq, India, Azerbaijan, Pakistan, Myanmar, Afghanistan, and Israel in Asia; Albania, France, and Sweden in Europe; and Nigeria, Cameroon, and Niger in Africa; as well as in wild birds in some 24 countries across Asia and Europe. In 2003, over 25,000,000 birds were slaughtered because of 241 outbreaks of HPAI caused by virus of H7N7 subtype in the Netherlands. The virus spread into Belgium (eight outbreaks) and Germany (one outbreak). HPAI H5N2 virus was responsible for outbreaks in ostriches in South Africa during 2005. HPAI H7N3 virus was isolated in Pakistan in 2004. Low-pathogenicity avian influenza (LPAI) H5 or H7 viruses were isolated from poultry in Italy (H7N3 2002–2003; H5N2 2005), the Netherlands (H7N3 2002), France (H5N2 2003), Denmark (H5N7 2003), Taiwan (H5N2 2004), and Japan (H5N2 2005). Many isolations of LPAI viruses of other subtypes were reported from domestic and wild birds. Infections with H9N2 subtype viruses have been widespread across Asia during 2002–06.

Gordon Memorial Lecture. Newcastle disease.

1. In this paper several historical and contemporary aspects of Newcastle disease (ND) are reviewed, with particular reference to the greater understanding which modern techniques have allowed. 2. Virulent ND viruses were generally thought to have emerged in 1926 as a result of transfer from a wild bird host reservoir but there is evidence that the virulent virus may have existed in poultry before 1926. Recent findings suggest that the virulent virus may emerge in poultry as a result of mutations in viruses of low virulence. 3. The history of ND in Great Britain reflects the four known panzootics that have occurred and serves as a model for the impact this disease may have on poultry populations. 4. Attempts to control and eradicate ND are not as straightforward as it may appear; in particular vaccination, while preventing deaths and disease, on challenge may not prevent virus replication and could therefore lead to the virulent virus becoming endemic. 5. Village chickens are extremely important assets in most developing countries, representing a significant source of protein in the form of eggs and meat but endemic ND can cause mortality of up to 60% in village chickens.

Experimental assessment of the pathogenicity of eight avian influenza A viruses of H5 subtype for chickens, turkeys, ducks and quail.

Clinical signs, death, virus excretion and immune response were measured in 2-week-old chickens, turkeys, quail and ducks infected by intramuscular, intranasal and contact routes with eight influenza viruses of H5 subtype. Six of the viruses: A/chicken/Scotland/59 (H5N1), ck/Scot; A/tern/South Africa/61 (H5N3), tern/SA; A/turkey/Ontario/ 7732/66 (H5N9); ty/Ont; A/chicken/Pennsylvania/1370/83 (H5N2); Pa/1370; A/turkey/Ireland/83 (H5N8); ty/Ireland, and A/duck/Ireland/ 113/84 (HSN8); dk/Ireland, were highly pathogenic for chickens and turkeys. Two viruses, A/chicken/Pennsylvania/1/83 (H5N2), Pa/1 and A/turkey/Italy/ZA/80 (H5N2), ty/Italy, were of low pathogenicity. Ck/Scot was more pathogenic for chickens than turkeys while ty/Ont was more pathogenic for turkeys than chickens. Other viruses showed little difference in their pathogenicity for these two hosts. No clinical signs or deaths were seen in any of the infected ducks. Only two viruses, dk/Ireland and ty/Ireland, produced consistent serological responses in ducks, although intramuscular infection with tern/SA and ty/Italy resulted in some ducks with positive HI titres. These four were the only viruses reisolated from ducks. Quail showed some resistance to viruses which were highly pathogenic for chickens and turkeys, most notably to ck/Scot and ty/Ont and to a lesser extent tern/SA and Pa/1370. Transmission of virus from intranasally infected birds to birds placed in contact varied considerably with both host and infecting virus and the various combinations of these.

A review of RT-PCR technologies used in veterinary virology and disease control: sensitive and specific diagnosis of five livestock diseases notifiable to the World Organisation for Animal Health

Real-time, reverse transcription polymerase chain reaction (rRT-PCR) has become one of the most widely used methods in the field of molecular diagnostics and research. The potential of this format to provide sensitive, specific and swift detection and quantification of viral RNAs has made it an indispensable tool for state-of-the-art diagnostics of important human and animal viral pathogens. Integration of these assays into automated liquid handling platforms for nucleic acid extraction increases the rate and standardisation of sample throughput and decreases the potential for cross-contamination. The reliability of these assays can be further enhanced by using internal controls to validate test results. Based on these advantageous characteristics, numerous robust rRT-PCRs systems have been developed and validated for important epizootic diseases of livestock. Here, we review the rRT-PCR assays that have been developed for the detection of five RNA viruses that cause diseases that are notifiable to the World Organisation for Animal Health (OIE), namely: foot-and-mouth disease, classical swine fever, bluetongue disease, avian influenza and Newcastle disease. The performance of these tests for viral diagnostics and disease control and prospects for improved strategies in the future are discussed.

Phylogenetic analysis of H7 haemagglutinin subtype influenza A viruses

Summary. A 945 nucleotide region (bases 76–1020) of the HA1 part of the HA gene was obtained for 31 influenza viruses of H7 subtype isolated primarily from Europe, Asia and Australia over the last 20 years. These were analysed phylogenetically and compared with sequences of the same region from 23 H7 subtype viruses available in Genbank. The overall results showed two geographically distinct lineages of North American and Eurasian viruses with major sublineages of Australian, historical European and equine viruses. Genetically related sublineages and clades within these major groups appeared to reflect geographical and temporal parameters rather than being defined by host avian species. Viruses of high and low virulence shared the same phylogenetic branches, supporting the theory that virulent viruses are not maintained as a separate entity in waterfowl.

H7N1 avian influenza in Italy (1999 to 2000) in intensively reared chickens and turkeys

From the end of March to the beginning of December 1999, an epidemic of low pathogenicity avian influenza (LPAI) affected the industrial poultry population of northern Italy. The virus responsible for the epidemic was subtyped as H7N1 with an intravenous pathogenicity index (IVPI) of 0.0, and a deduced amino acid sequence of the region coding for the cleavage site of the haemagglutinin molecule typical of low pathogenicity viruses. The circulation of the virus in a susceptible population for several months caused the emergence of a highly pathogenic virus with an IVPI of 3.0 and the presence of multiple basic amino acids in the deduced amino acid sequence for the cleavage site of the haemagglutinin molecule. Over 13 million birds were affected by the epidemic and, in the present paper, we report the results of the clinical, virological and histopathological investigations performed on affected chickens and turkeys. Clinical, gross and microscopic lesions caused by LPAI were more severe in turkeys than in chickens, while highly pathogenicity avian influenza (HPAI) caused similar mortality rates in both species. Current European legislation considers LPAI and HPAI as two completely distinct diseases, not requiring any compulsory eradication policy for LPAI but enforcing eradication for HPAI. In the Italian 1999 to 2000 epidemic, LPAI mutated to HPAI in a densely populated area, causing great economic losses. A reconsideration of the current European Union legislation on avian influenza, including LPAI of the H5 and H7 subtypes, could possibly be an aid to avoiding devastating epidemics for the poultry industry.